Limestone is calcareous sedimentary rock, which is composed of the mineral calcite (CaCO3). Upon calcinations, Limestone yields lime (CaO) for commercial use. The main source of Limestone is the limy ooze formed in the ocean. The rock, which contains containing more than 95% of Calcium Carbonate, is termed high-calcium Limestone. Recrystallised limestone, when properly polished, is used as a decorative building stone, called Marble. With acids, Limestone can easily be dissolved.